The following background information is provided to assist the reader to understand the environment in which the invention will typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless specifically stated otherwise in this document.
As shown in FIG. 1, a typical freight train 1 includes one or more locomotives 2, a plurality of railcars 3 and a pneumatic trainline known as the brake pipe 4. For a freight train headed by a locomotive equipped with a conventional pneumatic brake control system, the brake pipe 4 is the only means by which service and emergency brake commands are conveyed from the lead locomotive to each railcar in the train.
The brake pipe 4 is essentially one long continuous tube that runs from the lead locomotive to the last railcar in the train. As shown in FIG. 2, it is actually composed of a series of pipe lengths 4a, with one pipe length secured to the underside of each railcar. At the end of each pipe length is a glad hand 7. The brake pipe 4 is formed by coupling the glad hand 7 on the end of each pipe length 4a to the glad hand of another such pipe length on an adjacent rail vehicle. It is to this brake pipe 4 that the pneumatic brake equipment on each railcar connects via a branch pipe 8. As is well known in the railroad industry, by moving the automatic brake handle 21 located in the locomotive, the train operator can control how much, if any, pressure is contained within the brake pipe 4 and thus whether, and to what extent, the train brakes will be applied. The positions into which the brake handle can be moved include release, minimum service, full service, suppression, continuous service and emergency. Between the minimum and full service positions lies the service zone wherein each incremental movement of the handle 21 toward the full service position causes the brake pipe pressure to reduce incrementally.
The pneumatic brake equipment on each railcar includes two storage reservoirs 9 and 19, one or more brake cylinders 11 and at least one pneumatic brake control valve 12 such as an ADB, ABDX or ABDW type valve made by the Westinghouse Air Brake Company (WABCO). The pneumatic brake control valve 12 has a service portion 13 and an emergency portion 14 mounted to a pipe bracket 15. The pipe bracket 15 features a number of internal passages and several ports. Each port connects to one of the interconnecting pipes from the railcar such as those leading to the brake pipe 4, the brake cylinder 11 and the two reservoirs 9 and 19. It is through the ports and internal passages of the pipe bracket 15 that the service and emergency portions of the brake control valve 15 communicate fluidly with the pneumatic piping on the railcar.
It is well known that the pressure level within the brake pipe 4 determines whether the brake control valve 12 will charge the reservoirs 9 and 19 or deliver pressurized air previously stored in one or both of these reservoirs to the brake cylinders 11. By changing the pressure within the brake pipe 4, the brake pipe can be used to convey release, service and emergency brake commands to the pneumatic brake equipment on each railcar in the train. In response to a release brake command (i.e., when brake pipe pressure is restored to its maximum level as set by the train operator), the service portion 13 of brake control valve 12 not only charges the two reservoirs 9 and 19 with the pressurized air it receives from the brake pipe 4 but also vents the brake cylinders 11 to atmosphere thereby causing the brakes on the train to release. In response to a service brake command (i.e., when brake pipe pressure is reduced at a service rate), the service portion 13 supplies air from only one of the two reservoirs to the brake cylinders 11 so as to apply the train brakes. How much the brake pipe pressure is reduced, and thus the magnitude of the service brake application, depends on how far the handle 21 is moved towards the full service position. In response to an emergency brake command (i.e., when the brake pipe pressure is reduced to zero at an emergency rate), the emergency portion 14 of brake control valve 12 supplies air from both reservoirs 9 and 19 to the brake cylinders 11 so as to apply the train brakes fully. The emergency portion 14 also accelerates the pressurizing of the brake cylinders 11 by venting the brake pipe 4 on the railcar.
On each railcar and locomotive, each brake cylinder 11 converts to mechanical force the pressurized air it receives from its corresponding brake control valve 12. From the brake cylinders this force is transmitted by mechanical linkage (not shown) to the brake shoes (not shown) causing the brake shoes to be forced against, and thus to stop or slow the rotation of, the wheels of the rail vehicle. The magnitude of the braking force applied to the wheels is directly proportional to the pressure built up in the brake cylinders 11. For a freight train equipped with the conventional pneumatic brake system, it is thus the pressure level within the brake pipe 4 that determines whether and to what extent the brakes will be applied.
For a train headed by a locomotive equipped with an ECP (electrically controlled pneumatics) based brake control system, release, service and emergency brake commands are conveyed electrically to the ECP brake - equipment on each railcar of the train via a two wire ECP trainline (not shown). The ECP brake equipment (not shown) on each railcar is essentially the same as the railcar brake equipment previously described, except for the service portion 13 of the brake control valve. As is well known in the art, a car control unit (CCU), one or more pressure transducers and various pneumatic and electropneumatic valves are used in lieu of the service portion. The pressure transducers are used to monitor pressure in the brake pipe and the brake cylinders as well as the pressure in the two reservoirs. Supplied from a 74V dc power line of the MU cable in the locomotive, the ECP trainline operates at a nominal 230V dc to provide power to the ECP brake equipment on each railcar.
In a manner well known in the railroad industry, by moving the brake handle of the master controller in the locomotive, the train operator can transmit along the ECP trainline the desired brake command to the ECP brake equipment on each railcar in the train. Controlled ultimately from the locomotive, each CCU is connected via branch wiring to the ECP trainline from which it receives the electrical brake commands issued by the master controller. The degree of brake application ordered by the master controller is typically conveyed in terms of a percentage of the brake cylinder pressure required for a full service application of the brakes. For example, zero percent (0%) is typically designated for a release of the brakes, 15% for a minimum service brake application, 100% for a full service brake application and 120% for an emergency application of the brakes. According to the dictates of the particular electrical brake command transmitted from the locomotive, each CCU controls its electropneumatic valves through which pressurized air can be supplied to or exhausted from the brake cylinders under its control.
For railcars equipped with ECP brake equipment, the brake pipe still serves as the source of pressurized air from which to charge the reservoirs on each railcar when the brakes are released. During service and emergency braking, it is still from one and both reservoirs, respectively, that pressurized air is delivered to the brake cylinders to apply the railcar brakes. In the ECP brake control system, however, the brake pipe is not used to convey service brake commands. It is used only to convey emergency brake commands as a pneumatic backup to the electrical emergency brake commands conveyed by the master controller along the ECP trainline. Should a loss of power or other critical electrical failure occur, the ECP brake equipment is designed to respond pneumatically to an emergency pressure reduction in the brake pipe 4 by supplying pressurized air from both reservoirs to the brake cylinders 11 thereby causing an emergency application of the brakes under its control.
Many trains, whether equipped with conventional or ECP brake control systems, are also rigged with any one of several known end-of-train (EOT) radio telemetry systems. These systems include a locomotive control unit (LCU) in the locomotive and an EOT unit on a railcar, typically the last railcar, in the train. Also referred to as a head of train (HOT) unit, the LCU is mounted to the train operator's console in the locomotive. Mounted to the last railcar, the EOT unit is coupled to the brake pipe 4 by means of a hose and a glad hand.
In a one-way EOT system, the EOT unit transmits to the HOT unit via radio signals data pertaining to the pressure in the brake pipe and the motion of the last railcar. To accomplish this, the EOT unit includes a pressure transducer to monitor brake pipe pressure, a motion sensor to sense movement of the railcar, a microprocessor unit to control the overall operation of these components, and a transmitter that the microprocessor unit uses to transmit this last railcar data. In the locomotive, the HOT unit includes a receiver to receive transmissions from the EOT unit, a primary display and a microprocessor unit to direct the operation of these components. Using the last railcar data it receives from is the EOT unit, the HOT unit thus continuously updates the train operator with the status of operations at the rear of the train. More notably, if a potentially dangerous situation arises such as the brake pipe pressure plunges suddenly or drops below a predetermined level, the HOT unit operates to warn the train operator that an emergency condition exists at the rear of the train.
For a train equipped with a one-way EOT system, the emergency brake application starts at the locomotive and progresses along the brake pipe to the last railcar. For long trains, reducing the pressure in the brake pipe from the head of the train can be quite time consuming, particularly for a train equipped with a conventional pneumatic brake control system. Moreover, if one of the angle cocks 5 is left closed or the brake pipe 4 is otherwise restricted, the brake equipment beyond the restriction may not receive the emergency brake command needed to apply the brakes in an emergency. For this reason, two-way EOT systems have been developed under the auspices of the American Association of Railroads (AAR).
In a two-way EOT system such as the TRAINLINK.RTM. II EOT system manufactured by WABCO, the HOT and EOT units still perform all of the functions attributed to their counterparts in the one-way EOT system. As shown in FIG. 1, the EOT unit 55 is thus still used to transmit the aforementioned radio signals by which last railcar brake pipe pressure and motion data is conveyed to the HOT unit 51. The two-way EOT and HOT units, however, are each equipped with a transceiver (i.e., combination transmitter and receiver) as compared to the single transmitter and receiver for the one-way EOT and HOT units, respectively. The EOT unit 55 also has an emergency brake valve that is controlled by its microprocessor unit, and the HOT unit 51 also includes an emergency toggle switch. By toggling this switch in an emergency, the train operator can cause the HOT unit 51 to transmit an emergency brake radio signal to the EOT unit 55. By its microprocessor unit, the EOT unit responds to this emergency signal by commanding its emergency brake valve to reduce the pressure in the brake pipe at an emergency rate. Combined with the emergency reduction in brake pipe pressure initiated from the head end of the train using the aforementioned locomotive brake equipment, the two-way EOT system allows an even faster application of the railcar brakes in an emergency.
In this two-way EOT system, the HOT unit has a primary display panel which features a dedicated display for each of several types of last railcar data. The last railcar data displayed includes brake pipe pressure, low battery condition, whether the railcar is stopped or in motion, and whether an emergency has been enabled or disabled. The HOT unit 51 also has a supplemental message display by which it visually conveys additional information such as, for example, data related to arming of the EOT system and whether or not the EOT and HOT units are communicating properly.
For a train equipped with a conventional pneumatic brake control system wherein the brake pipe 4 is used to pneumatically convey both service and emergency brake commands to the railcars, another EOT radio telemetry system, such as the TRAINLINK.RTM. ES system manufactured by WABCO, may be used. It is, of course, well known that an emergency application is initiated at a rate much faster than a service application. Typically, the emergency reduction in pressure propagates along the brake pipe at a speed of approximately 900 feet/sec. Consequently, for a one mile long train, the propagation time would be in the range of 10 to 15 seconds. In contrast, a service application can take well over a minute to reach the last railcar; hence the need for, and development of, the TRAINLINK.RTM. ES system.
In addition to the two-way HOT and EOT units, the TRAINLINK.RTM. ES system has a Service Interface Unit (SIU) 52 that connects between the serial port of the ES HOT unit 51 and the brake pipe on the locomotive. The SIU 52 provides the ES HOT unit 51 with the current brake pipe pressure. This allows the ES HOT unit 51 to automatically initiate a service brake application at the last railcar simultaneously with the service reduction in brake pipe pressure initiated from the locomotive. Specifically, the ES HOT unit 51 in the locomotive 2 automatically transmits a service brake radio signal to the ES EOT unit 55 when it detects a service reduction in brake pipe pressure via the SIU 52. By its microprocessor unit, the two-way ES EOT unit 55 responds to this service brake signal by commanding its emergency valve to reduce the brake pipe pressure from the last railcar at the same service rate as that ordered by the locomotive brake equipment at the head of the train. A service application of the brakes can thus be made much faster on a train equipped with a TRAINLINK.RTM. ES or similar type EOT system. Using the SIU, the ES HOT unit can also automatically transmit an emergency brake signal when an emergency reduction in brake pipe pressure has been initiated by the locomotive brake equipment. The emergency toggle switch on the ES HOT unit can also be used to transmit this emergency brake signal.
As is well known in the railroad industry, two-way EOT systems employ an authorization protocol. After railcars are coupled to the locomotive(s) to form a train and before that train is put into service, the train operator must arm or authorize the HOT unit 51 in the lead locomotive 2 to communicate only with the EOT unit 55 on that particular train. The authorization protocol prevents an HOT unit 51 on one train from being erroneously or maliciously used to apply the brakes on another train. To this end, the HOT unit 51 includes a thumb wheel switch assembly and a nonvolatile memory in which an identification code unique to a particular EOT unit can be stored. With that EOT unit on the last railcar, only when the train operator sets the thumb wheel switches to correspond to the EOT identification code stored in its memory is the HOT unit authorized to communicate with the EOT unit on the train. The HOT unit retains in its memory the identification code for that particular EOT unit until armed for a different EOT unit.
To authorize the HOT unit to communicate with a different EOT unit, a railroad employee pushes a test button on the new EOT unit so that it will transmit a first authorization signal. This signal contains the identification code of the EOT unit along with a special message identifier and confirmation bit. When the HOT unit 51 receives the transmission, it displays an ARM NOW message if the stored code differs from the identification code of the new EOT unit. By manually pushing the COMM TEST/ARM button on the HOT unit 51 within six seconds of the ARM NOW message being displayed, the train operator initiates a status update request (SUR). If the EOT unit receives the SUR within six seconds from the time the EOT test button was pushed, the EOT unit responds by transmitting a second authorization signal. This signal contains a special message identifier and confirmation bit. Upon receiving the EOT unit's response, and if its thumb wheel switches have been set to the identification code of the new EOT unit, the HOT unit 51 then displays the ARMED message and stores in its nonvolatile memory the identification code of the new EOT unit thereby overwriting the previously stored code. This procedure for arming the EOT system is more fully set forth in the 1989 Communications Manual, Parts 12-15, pp. 38-39, published by the AAR. Moreover, another procedure for arming the EOT system, among others known in the art, is taught in U.S. Pat. No. 5,016,840, incorporated into this document by reference.
Before the invention presented in this document, the only way to test whether an EOT unit 55 was working properly was to use an HOT unit 51. The problem is that an HOT unit 51 is a stationary, non-portable device, one that is enmeshed with the other equipment in the locomotive. Consequently, in order to test whether an EOT unit 55 is operating properly, one must essentially assemble a train first. Specifically, one must first install the subject EOT unit 55 on a railcar inclusive of the connections to the brake pipe 4, and then couple that railcar, inclusive of the brake pipe connections, to a locomotive. The locomotive, of course, must be equipped with the HOT unit appropriate for the subject EOT unit under test (e.g., only a TRAINLINK.RTM. ES type HOT unit can be used to completely test an EOT unit designed to respond to both service and emergency brake radio signals). Next, not only must the locomotive be powered up, but the brake pipe 4 of the train 1 must also be leak-tested and then charged to its maximum set-up pressure. The resulting two-way EOT system can then be armed using the appropriate arming procedure. Only after the two-way EOT system is armed is the EOT unit ready to be tested to determine whether it properly responds to the brake signal(s) transmitted by its corresponding HOT unit.
The actual testing of the EOT unit, inclusive of the arming procedure, is a very laborious task. The arming procedure set forth by the AAR requires two individuals, one at the HOT unit in the locomotive and the other at the EOT unit on the railcar, working in concert to arm the EOT system. Testing the functions of the EOT unit also requires two people. For example, the operator in the locomotive must cause the HOT unit to transmit the applicable brake radio signal to the EOT unit. The railyard worker at the EOT unit must then verify whether the EOT unit has actually responded to the signal by venting the brake pipe. Though the arming procedure described in U.S. Pat. No. 5,016,840 requires just the operator at the HOT unit, the testing of the EOT unit still involves substantial labor. For example, once the EOT system is armed, either the train operator in the locomotive or a second person altogether must go to the end of the train to verify that the EOT unit has responded to the brake radio signal by venting the brake pipe according to the dictates of the particular brake signal received.
The main disadvantages of these prior art ways of testing an EOT unit are that they require substantial investments of time and labor. Prior to the invention presented below, no device had been proposed that would allow the EOT unit to be tested outside the environment in which it operated. Specifically, the lack of such a testing device had meant that a train (i.e., at least one locomotive and one railcar) first had to be assembled, with the EOT unit to be tested installed on the railcar. Next, the resulting EOT system had to be armed and then the EOT unit tested as noted above. The lack of such a testing device meant that there was no simple and less laborious and time consuming way of testing an EOT unit.
Another shortcoming related to the current practice of testing a two-way EOT system often arises in the assembly of long freight trains. It is, of course, advisable to test the EOT system before the train is to begin its run. Unfortunately, the radio link between the HOT and EOT units may not be able to be established until after the train has departed due to the terrain of the railyard or other area in which the train is assembled. The topography of the assembly area may have natural or man-made obstructions that block or interfere with the transmission and reception of the radio signals. The invention described and claimed below--a portable test device--is intended to address these disadvantages and shortcomings.